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ABSTRACT
The current study presents the energy and exergy analysis of a thermoelectric waste heat recovery system of an automobile using an aluminum-based heat exchanger. The experiment was conducted on a 4 cylinder direct injection diesel engine by varying the load with constant engine speed. Effect of second law efficiency, availability, entropy generation along with output current, and power of the thermoelectric system on various engine loads have been considered and were compared. Furthermore, the CFD analysis of the heat exchanger of a waste heat recovery system has been considered to evaluate the optimal thickness at the inlet conditions of exhaust gas. On the basis of CFD analysis, the optimal thickness of 3 mm for the heat exchanger has been used for waste heat recovery. The maximum entropy generated by the designed waste heat recovery system is found to be significantly less than the entropy generated by the engine. However, the availability of the exhaust gas is 81.8% higher than the availability of coolant. The study revealed that significant energy is lost through the exhaust, and employing higher load with constant engine speed enhances the scope of waste heat recovery.
Nomenclature
| Symbol | = | Nomenclature |
| Qin | = | Input energy to the engine per unit time |
| Qshaft | = | Power available at the shaft of engine per unit time |
| Qcw | = | Energy taken away from engine by cooling water per unit time |
| Qe | = | Energy taken away as exhaust per unit time |
| Qun | = | Energy unaccounted per unit time |
| Ain | = | Input availability to the engine per unit time |
| Ashaft | = | Availability at the shaft of engine per unit time |
| Acw | = | Availability taken away from engine by cooling water per unit time |
| Ae | = | Availability in exhaust per unit time |
| Ad | = | Destructed availability |
| Qi,hx | = | Input exhaust energy to the heat exchanger per unit time |
| QTEG | = | Energy produced by TEG per unit time |
| Qco | = | Energy taken by coolant from the cold side of TEG per unit time |
| Qo,hx | = | Exhaust energy from the heat exchanger per unit time |
| Ai,hx | = | Availability of exhaust inlet to heat exchanger per unit time |
| ATEG | = | Availability as power produced by TEG per unit time |
| Ao,hx | = | Exhaust availability from the heat exchanger per unit time |
| Pamb | = | Ambient pressure |
| Pe | = | Exhaust gas pressure |
| Tamb | = | Ambient temperature |
| Cp,co, Cp,cw | = | Specific heat capacity of the cooling coolant Specific heat capacity of cooling water |
| Cp,ex | = | Specific heat capacity of exhaust gas |
| Tamb | = | Ambient temperature |
| Tcw,o | = | Temperature of cooling water outlet from the engine |
| Tcw,i | = | Temperature of cooling water inlet to the engine |
| Tex,ih | = | Temperature of exhaust gas from engine inlet to EHX |
| Tex,oh | = | Temperature of exhaust gas outlet from EHX |
| Tco,o | = | Temperature of coolant outlet from cold side of a thermoelectric generator |
| Tco,i | = | Temperature of coolant inlet to the cold side of a thermoelectric generator |